High Step-down Two-stage DC/DC Converter for Low Voltage Battery Charger

In electric vehicles (EVs), low-voltage DC/DC battery chargers (LDCs) play a critical role in addressing the rising power demands in EVs. This paper studies a two-stage DC/DC converter design, combining a Buck converter and an LLC converter to effectively power the modern 800V EV battery. The converter aims to deliver 3.5kW at 13.6V, serving the high-power requirements of EV appliances such as sound system, display system, and air conditioning system. The first stage, a Buck converter, employs Discontinuous Conduction Mode (DCM), featuring a simple switch and diode configuration to reduce losses. The second stage, an LLC converter, operates at its resonant frequency to achieve optimal efficiency, utilizing an asymmetric half-bridge topology. Detailed analysis of the selected topology and transformer design, along with simulation results, are provided to validate the proposed system's efficacy.